This invention relates to a system for removing particles from exhaust produced by an internal combustion engine, such as a diesel engine.
Exhaust produced by diesel engines has a relatively high content of polluting particles composed of carbon, unburned fuel, and partially burned fuel. Filters or traps are conventionally disposed in engine exhaust systems to remove the particles from the exhaust. In this case, burners positioned in the exhaust systems upstream of the filters are usually employed to burn off particles deposited on the filters to unclog and rejuvenate the filters.
An exhaust particle removing system including such a filter and a burner has been proposed. This system also includes a pressure sensor which monitors the pressure across the filter as an indication of the degree of clogging of the filter. Furthermore, this system includes a device which determines a pressure reference level on the basis of engine operating conditions, such as engine speed and engine load.
When the monitored pressure exceeds the reference level, fuel supply to the burner is commenced and an igniter of the burner is energized to activate the burner. If ignition of the supplied fuel fails, the operations necessary to activate the burner are repeated. If ignition of the supplied fuel succeeds, activation of the burner is maintained for a preset duration necessary to completely unclog the filter. After this duration, the burner is deactivated. A temperature sensor detects whether the fuel ignition has failed or succeeded by monitoring the temperature difference between positions upstream and downstream of the burner.
Such a conventional exhaust particle removing system can not compensate for variations and tolerances of the characteristics of the pressure sensor resulting from ageing and individual deviations thereof respectively. Accordingly, this system can not accurately determine the pressure across the filter, resulting in commencement of unwanted activation of the burner and/or failure of commencement of necessary activation of the burner, in turn causing unreliable and unacceptable removal of the particles from the exhaust.